Sterilizer test device

ABSTRACT

A re-usable sterilizer test device is disclosed which is comprised of at least two parts which are releasably connected together. An indicator device which changes colour in the presence of steam after a certain time period is deposited within the two parts. One or both of the bodies is manufactured from a material having a predetermined degree of porosity as regards steam and is generally cylindrical or spherical so that the outer surface of said one or both bodies forms a significant and substantial portion of the external surface of the assembled device. Steam penetrates the porous body and passes into a cavity inside the body from where the steam can move internally of the device through suitable passageways and into a chamber where the indicator is located.

This invention relates to a sterilizer test device.

Almost all hospitals in the western world are provided with sterilizingequipment to ensure the sterility of instruments and devices which maycome into contact with humans. The risks and dangers of conductingoperative procedures on living creatures including animals and humanswith non-sterile equipment and in non-sterile surroundings is welldocumented. In an environment in which patients expect to be treatedsuccessfully and in a sterile manner, the requirement for effectivesterilization is an essential one, and devices have been developed totest the efficacy of sterilizers and sterilization.

Although the following description relates exclusively to the use ofsterilizer test devices in hospitals, the device of the presentinvention has much wider application, and specifically can be used inbench top sterilizers such as might be provided in community healthcareand animal care clinics for the sterilization of utensils, dressings,medical textiles and the like.

Modern sterilizers, many of which are in the form of high pressureautoclaves, subject their contents to high temperature steam for apredetermined period of time. The three fundamental parameters of thesterilization process are accordingly time, temperature, and thepresence of steam. Effective sterilization can only be achieved if thereis steam contact with all parts of the load to be sterilized for thecorrect period of time. Air trapped and entrained within the load willprevent this necessary steam penetration. The thermodynamicirregularities of air/water vapour mixtures, and the necessarily hostileenvironment developed inside cabinet autoclaves makes the monitoring ofsterilization process difficult, and therefore a simple visual indicatortest was developed.

In the 1960s, the Bowie Dick test assessed whether the air removal stageof the sterilization process was sufficient to ensure rapid and evensteam penetration to all parts of the load. The test involved placingwithin the sterilizer a stack of towels approximately 11 inches high andhaving a cross-sectional area roughly approximating to the size of an A4sheet of paper. Within the stack at approximately half height thereof,there was placed a sheet of paper on one surface of which was applied apattern of a chemical indicator ink which was extremely sensitive to andchanged colour in the presence of high temperature steam. The test wasperformed by simply placing the stack towels within the sterilizer, andinitiating a standard cycle of the sterilizer which would be carried outon, for example a tray of surgical instruments, hospital bed linen andthe like, for a certain period of time, for example 3-4 minutes. Onremoval of the stack of towels, the indicator sheet was inspected for auniform colour change of the indicator over the entire surface of thesheet, and if this was the case then the sterilizer air removal stagewas considered to be functioning effectively.

It is well known that heat alone can provide effective sterilization,however the rapid inactivation of microorganisms is significantly fasterin the presence of moist heat (steam). For example, effectivesterilization can be achieved by subjecting material to dry heat at 160°C. for 1 hour, whereas the same level of sterilization can be achievedby introducing steam at 130° for 3 minutes. In the Bowie Dick test, thetowels were used as what is now termed a “porous load”. Such loads aredeemed one of the most difficult to assess the penetrationcharacteristics of the steam or to provide some resistance to the steamas it progresses towards the indicator sheet. The rationale behind thistest is that if the steam can penetrate the porous load to adequatelychange the colour of the indicator sheet, then any medical device,textile or the like having a lower resistance to steam penetration willbe effectively sterilized.

A current modification of the original Bowie & Dick test is the use of adisposable or reusable barrier surrounding a chemical indicator sheet.This is calibrated to perform in a similar manner to the original Bowie& Dick towel pack with a chemical indicator inserted. After the pack hasbeen subjected to a conventional sterilization, the indicator sheet isremoved and inspected for a uniform colour change over the entiresurface area of the sheet, which is indicative of the effectiveoperation of the sterilizer air removal stage.

A disadvantage with this method of testing is that the product once usedmust be discarded. When it is considered that millions of tests areconducted annually in hospitals and other sterile environments aroundthe world, the cost saving to be made by a reusable device may beconsiderable.

One alternative currently available to the disposable test packdescribed above is a device which comprises a coiled narrow lumenapproximately 2-3 metres in length and having a diameter ofapproximately 2 mm, open at one end and connected at its alternate endto a small accessible capsule into which a chemical indicator can beplaced. In use, the coiled lumen is placed inside the sterilizerwhereafter the sterilization procedure is initiated during which thesteam gradually progresses along the interior of the lumen untilreaching the capsule into which the lumen passes. The efficacy of steampenetration can be assessed based on the chemical indicator result.Thereafter, the device may be reused, using a new indicator in thecapsule.

The length and narrow entrance of the lumen open end render the lumenarguably not analogous to a porous load for reasons of mass, directionalsensitivity, and physical shape etc.

Hence there are a number of serious disadvantages associated with thelumen device. Firstly, the history of use of the device cannot easily beestablished and although the chemical indicator may be replaced beforeeach use of the device, there is no guarantee that the device was notpreviously mistreated or was not fully prepared for the next use by theprevious user. It is to be borne in mind that in a busy hospital, thedevice may simply left proximate the sterilizer for use by any of thenumerous staff who have cause to use same.

Secondly, there is a risk that the openable capsule is not securelyclosed. This would allow the steam an easier path to the open end of theindicator tube within the capsule, and thus the device could give thefalse indication that the sterilizer was functioning satisfactorily.

Thirdly, steam has a propensity to condense on the external, and moreimportantly the internal walls of the lumen. If sufficient steamcondenses of the internal wall of the lumen along the path to thecapsule, there may be a plug of condensate which could prevent the steamfrom reaching the open ended indicator tube within the capsule.

Fourthly, the problem of condensation is also apparent when the lumen isremoved after the test has been completed, and in some cases there canbe a fine mist of water vapour or a fluid bubble retained within thelumen. When a subsequent test is conducted, the lumen is heated in thesterilizer and by means of conduction, this water vapour could also heatand be urged towards the chemical indicator within the capsule. Thedevice could in this circumstance also provide false results.

Finally, it is contended by many of those in the art that the singlenarrow opening through which the steam passes before travelling thelength of said lumen is too directionally sensitive, that is it does notprovide a fair average of the steam penetration characteristics withinthe sterilization chamber.

Examples of directionally sensitive sterilization test devices are shownin consecutive published patent applications PCT/DE94/00687,PCT/DE94/00688, PCT/DE94/00689, all to Van Dijk Medezintechnik GmbH. Allthese documents disclose essentially cylindrical hollow test devices,one end of which is closed off from the atmosphere by means of a plug orstopper proximate to which a chemical indicator means is positioned inan inner chamber of the device, the alternate open end of the deviceshaving different inserts provided therein to provide a penetrablebarrier through which steam must pass to interact with the chemicalindicator within the device.

In particular, PCT/DE94/00687 discloses the use of a threaded plug whichis screwed into the open end of the device but which has threads ofmarginally lesser diameter than those provided internally of the devicesuch that a helical channel is defined between the threads of the plugand those of the device. This device is effectively similar to the lumendevice disclosed above, with the exception that a fixed helical pathleads from the exterior of the device to the chemical indicator, asopposed to the spiral path along which the steam can travel within thelumen.

PCT/DE94/00688 discloses the use of an array of capillaries providedbetween the inner chamber of the device in which the indicator islocated and the alternate open end of the device from which the steamwithin a sterilizer can penetrate, and PCT/DE94/00689 discloses the useof a porous material plug through which the steam can penetrate towardsthe indicator located in the inner chamber of the device. Neither ofthese latter two patent applications is specifically directed towardsthe use of a so-called “tortuous path” such as is provided by thehelical path disclosed in PCT/DE94/00687 or the spiral path along whichthe steam travels in the lumen of the abovementioned current devices,whereas PCT/DE94/00687 does not consider the use of a so-called “porousload”.

Additionally, all the devices disclosed in the abovementioned patentapplications are directionally sensitive in that steam can only begin topenetrate either the tortuous path or the porous load (or equivalentload) from one particular side, and furthermore only on one particularsurface of the device. It is to be mentioned that the conditions withinautoclave units in general are extreme and nonuniform, and it ispossible that the directional sensitivity, which term is used todescribe the generally linear path along which the steam or othersterilant travels before coming into contact with the indicator, of suchdevices can result in the device producing false results.

It is an object of the present invention to provide a sterilizer testdevice which at least mitigates if not eradicates the disadvantages ofthe prior art devices, and which is furthermore reusable and combinesthe advantageous qualities of the devices mentioned.

According to the present invention there is provided a sterilizer testdevice comprising a pair of bodies releasably and sealably connectedtogether defining an internal primary chamber within the device to whichaccess is gained by disconnecting said bodies, at least one of saidbodies being essentially comprised of a porous element which allowspenetration of steam therethrough and into said primary chamber,indicator means being provided between said bodies at some locationwithin the primary chamber, said indicator means having a characteristicwhich changes while in the presence of steam and temperature after apredetermined time, characterised in that said porous element has one ormore external surfaces through which steam can penetrate in a pluralityof different directions.

Preferably intermediate tortuous path means is additionally providedinternally of the device and sealingly divides the primary chamber intotwo secondary chambers, a first secondary chamber being defined betweenthe tortuous path means and an inner surface of said at least one bodythrough which steam having permeated said body emerges, and a secondsecondary chamber being defined to the alternate side of said tortuouspath means from the first secondary chamber and having the indicatormeans disposed therein, said steam being constrained to flow into andaround said tortuous path means before emerging into the secondsecondary chamber and thence coming into contact with the indicatormeans.

Preferably the said at least one body is provided with a substantiallyarcuate outer surface. In one embodiment, the said at least one body ispreferably cylindrical.

Most preferably, the outer surface of the porous body is substantiallycontinuous around at least one axis of the device.

It is most preferable that the two bodies connected together to form thedevice have a predetermined degree of porosity, and furthermore it ispreferable that each of said two bodies is substantially hemispherical.

It is yet further preferable that at least one of the bodies is providedinternally with a cavernous recess to increase the effective volume ofthe primary chamber.

It is further preferable that the porous bodies are manufactured from asintered polypropylene material, which has the advantage that itsporosity can be varied according to requirements of a particular device,and also that it can be formed in any desired shape. In an alternativeembodiment, the porous bodies are manufactured from a spun bondedpolymer material, but the manufacturing process for such materials islimited in that only articles having certain geometric shapes (such as acylinder) can be produced because of the manner in which the polymericmaterial is spun.

It is yet further preferable that apertured diaphragm means is providedinternally of the primary chamber substantially across the base of oneof the said bodies thus defining a tertiary chamber with the surfaces ofthe cavernous recess in which steam having permeated the porous elementfrom a plurality of different directions can collect before passingthrough said aperture into either the remainder of the primary chamberor the first secondary chamber.

It is also to be mentioned that such an apertured diaphragm could beused to sealingly divide either the first or second secondary chamberand thus define first and second tertiary chambers from said secondarychambers, and that two apertured diaphragms could be used to divide boththe first and second secondary chambers as desired.

The division of the internal primary chamber into secondary and tertiarychambers has been shown experimentally to improve the overallperformance of the sterilizer text device as a whole. Not wishing to bebound by theory, it is believed that this enhancement of performance isachieved because of the facility for steam to collect in the volume ofthe secondary and tertiary chambers in use which removes the effects onperformance of the traditionally cyclical and intermittent operation ofmodern sterilizers, i.e. the alternate drawing of a vacuum and theintroduction of steam into the sterilizer during use to substantiallyeliminate air.

In a further aspect of the invention there is provided a tortuous pathmeans for use in a sterilizer test device of the type described above,said means comprising at least two substantially planar componentshaving an outer surface and an inner surface separated by theirthickness, said components being releasably connected together to bringtheir respective inner surfaces proximate one another, one or other orboth of said components being provided with patterned grooved means ontheir inner surfaces following a labyrinthine, spiral or other tortuouspath on said surface, one of said components being provided with anentry port leading from an outer surface of said component through thethickness thereof and opening at a particular location in said groovedmeans, characterised in that an intermediate member is sandwichedbetween the two components to sealingly close said grooved means anddefine a tortuous channel to at least one side of said intermediatemember.

Preferably an exit port is also provided to allow fluid to escape from aparticular location in the grooved means, or alternatively there isprovided a recess in said inner surface of one of said components inwhich indication means as described above can be deposited.

Preferably the intermediate member is compressible to ensure sealingformation of said channel.

Preferably grooved means are provided on the inner surfaces of bothcomponents and the sandwiching of the intermediate member forms channelswith each of said grooved means on either side of said member.

In a most preferred embodiment the components are hingedly connectedover at a portion of their respective edges.

It is also preferable that the entry port of one component opens intothe grooved means on the inner surface thereof proximate one end of saidgrooved means, and also that the exit port provided on the alternatecomponent opens into the said grooved means in that component proximateone end thereof.

Most preferably, the intermediate member is secured to the hingedconnection of the two components which ensures the correct positioningof said intermediate member when the said two components are releasablyconnected together.

It is yet further preferable that the intermediate member is providedwith an aperture therein which links respective tortuous channelsdefined by said intermediate member on either side thereof.

In a yet further preferable embodiment, a chamber is defined internallyof said tortuous path means in which steam can collect prior to beingurged along said tortuous path.

It will be immediately understood by those skilled in the art that theprovision of separable components having grooves brought together duringthe connection of the components to define respective channels with theintermediate compressible member allows for easy cleaning and airing ofthe grooved means. Hence, the device according to the invention can beboth readily aired and cleaned while nevertheless being re-usable.

When the tortuous path means are used in connection with the sterilizertest device described above, the steam first permeates the porous bodieswhich substantially constitute the device and then is constrained toflow into a chamber of the device and thence through the tortuous pathmeans before emerging therefrom into a further cavity in which isdisposed the indicator means. The particular indicator means used is notimportant, and the device can be calibrated for use with a variety ofdifferent indicator types, such as chemical, biochemical, biological. Itis also foreseen by the applicant that electronic sensing and detectionapparatus may be used in place of the indicator means to provideaccurate data logs on the characteristics of the atmosphere extant inthe device in any of the chambers-defined therein as a function of thetime after the commencement of any particular sterilization sequence.

The fundamental advantages of the present invention are firstly that theuse of cylindrical or hemi-spherical porous bodies to form the deviceallows steam to permeate into said bodies from any direction assubstantially the entire surface of these bodies are porous, andsecondly that the tortuous path means can be easily, simply, and quicklyopened up to allow for airing and drying of the tortuous path.Thereafter both the test device and the tortuous path means can bereused. Obviously a quadrangular porous body having two or more of itsexternal surfaces exposed to the steam to allow for penetration thereofwould function in a similar manner.

A specific embodiment of the invention is now given by way of examplewith reference to the accompanying Figures wherein:

DESCRIPTION OF THE DRAWING

FIG. 1 shows an exploded perspective view of a cylindrical test devicein accordance with the invention,

FIG. 1A shows a perspective view of an apertured diaphragm which may beused in conjunction with the invention, and

FIG. 2 shows an exploded perspective view of a spherical test device inaccordance with a different embodiment of the invention.

Referring firstly to FIG. 1 there is shown a sterilizer test deviceindicated generally at 2 comprising an annular base 4 which on which thedevice stands when within a sterilizer, a cylindrical porous body 6having a cavernous bore 8 provided therein of a depth less than that ofthe body 6 and chosen as required by the particular application. Abovethe body 6, a number of different components are provided to allow thedevice to function correctly. The first of these is an annular cap 10having formations 12, 14, 16, 18 which permit the rotating lockingconnection of other components above said cap.

It will be seen from the diagram that the cap 10 is provided both with acollar 20 which is chamfered around its outer surface shown at 22 and ismarginally greater in diameter than the body 6 over which it isdisposed. An annular inner surface 24 is provided at approximately themedian of the depth of the cap, and above and around the periphery ofsaid surface 24 there is provided an annular skirt 26 which defines acircular recess with the said surface 24. An aperture 28 allows steamwhich has permeated through the porous body 6 to pass from the uppersurface 30 thereof and from within the cavity 8 through the cap 10.

The apertured diaphragm 25 may be sealingly disposed either on the innersurface of the body 6 over the cavernous bore 8 or in the aperture 28 sothat a tertiary chamber is defined by said diaphragm and said cavernousbore internally of the body, as this has experimentally shown to improvethe performance of the device, that is to more accurately determine if aparticular sterilizer under test is efficacious.

In accordance with the invention there is provided a tortuous pathdevice consisting of three components 32, 34, 36 which are hingedlyconnected together around their circumferences at hinge means 38, 40, 42respectively. Specifically, the hinge means 38 is a protrusion, 40 is anaperture of marginally greater size than said protrusion and throughwhich said protrusion is fed before locating in a recess 42 in thecomponent 36 in which it is pinned by means of rod 44.

With specific regard to said components 32, 34, 36, the first and thirdcomponents 32, 36 are substantially planar and provided with spiralgrooves 46 in one surface (only shown in respect of component 32). Thesecond component 34 is an intermediate component ideally of acompressible material which is sandwiched between components 32, 36 onreleasably connecting same together and ideally sealingly forms spiralchannels with the said grooves provided in the surfaces of the first andthird components on either side thereof.

The first and third components 32, 36 are provided with apertures (oneof which is shown at 48 in the component 36) at their centres which formentry and exit ports to the spiral channels formed between saidcomponents. The intermediate component 34 is additionally provided withan aperture 50 which allows fluid communication between the channelformed in the component 32 on one side of component 34 and channelformed in component 36. Thus the fluid enters the spiral channel formedin the first component through the aperture in said component 32 at itscentre, and is subsequently constrained to spiral outwardly from saidcentre until reaching the aperture 50 (which is ideally located at theend of the spiral groove 46). The fluid can then move through theaperture 50 and into the second spiral channel and wherein it isconstrained to spiral inwardly towards the aperture 48 from which itultimately emerges.

The entire arrangement of the tortuous path device (32, 34, 36) isreceived in the upper recess defined in the cap 10 by the surface 24 andits peripherally surrounding skirt 26 and optionally locked thereinbehind suitable flanges provided on the skirt 26. As the device 2 isassembled, the pre-assembled tortuous device (32, 34, 36) may be simplydropped into said recess and rotated by means of thumb indentations (notshown) provided on the upper surface of component 38.

Once secured in place, an indicator (not shown or described in thisapplication as being considered beyond the scope hereof) is positionedabove the aperture 48, and a lid 52 having depending skirt 54 is securedto the device by interengagement of formations (not shown) provided onthe inner surface of said skirt 54 with the formations 12, 14, 16, 18provided on the cap 10. The device is then placed in a sterilizer whichis then activated, and after a conventional sterilization operation iscomplete the device is removed and opened for inspection of theindicator.

It is to be mentioned that the device may be inverted, the base 4dispensed with, and the lid 52 may be suitably designed to function as abase having an inner surface in which an indicator may be disposed. Interms of the wording of the claims appended hereto, the primary chamberinternally of the device is defined by the cavernous bore 8 and theinner surface of said lid 52 through the aperture 28. This chamber issealingly divided by the interposing of the tortuous path means (32, 34,36) on either side of which are defined first (on the side of thecavernous bore 8) and secondary (on the side of the lid 52 innersurface) chambers. The first secondary chamber may again be divided bythe interposing of the apertured diaphragm 25 as previously mentioned sothat a tertiary chamber is defined within the body 6 by said cavernousbore 8 and said diaphragm.

It is also to be mentioned that the device described with reference toFIG. 1 can be used as a sterilizer test device without the tortuous pathmeans described above. An indicator may simply be placed on the annularsurface 24 or within the lid 52 to which steam can gain access afterhaving first permeated the porous body 6.

Additionally the configuration of the device 2 is adapted to be furthermodified so that the porous body can be removed leaving only the base 4,cap 10, tortuous path means (32, 34, 36) and lid 52.

However, use of the complete device having both porous body and tortuouspath means is preferred.

Referring now to FIG. 2 there is shown a modified configuration ofsterilizer test device 100. The device comprises of a tortuous pathdevice (32, 34, 36) as hereinbefore described disposed internally of thedevice, and two hemispherical porous bodies 102, 104. Body 104 isprovided internally with a cavity 106 in which steam may collect, andthe portions of both bodies 102 proximate their diametral planes arereceived in the hingedly connectable skirt members 108, 110 having hingeformations shown at 112, 114.

As with the embodiment shown in FIG. 1, a suitably sized apertureddiaphragm may be used to define a chamber with said cavity 106 aspreviously discussed.

The skirt member 108 is provided with a plurality of slots 116, 118through which steam emerging from the planar surface 120 of body 102 canpass. When assembled together, the configuration is such that steampermeating through the body 102 passes to the outside of the tortuouspath device and towards and into the cavity 106 without coming intocontact with the indicator (not shown) which is disposed between theouter surface of the component 32 and the rear surface 122 of the cap108. The disposition of said indicator, possibly within a recess definedin said rear surface 122, and the clamping arrangement of the two capson the tortuous path device (32, 34, 36) thereover ensures that steamcannot adversely affect the indicator such that the device would giverise to false results.

In a similar manner to the operation of the device shown in FIG. 1, thedevice 100 can be easily and quickly opened and the tortuous path devicereleased from over the indicator which can then be inspected to ensurethat a sterilizer is functioning correctly. Additionally, the tortuouspath device can be removed quickly, and opened for drying and cleaning.

It is to be mentioned that the various arrows provided on the diagramsare indicative of the possible flow of steam from outside the devicesand the particular flow paths possible inside said device. It is mostimportant to note that both the devices disclosed herein are bothreusable and “directionless” in that steam drawn towards the deviceswhen inside an operative sterilizer can permeate through the porous bodyas soon as it comes into contact therewith. This is in sharp distinctionto the currently available devices which are either not re-usable orwhich although being of similar size and shape to the devices describedherein, generally provide only a few discrete ports through which accessto a porous medium is contained. Such devices are heavily directional,and therefore disadvantaged in comparison to the present invention.

1. A sterilizer test device comprising: at least a pair of bodiesreleasably and resealably connected together defining an internalprimary chamber within the device to which access is gained bydisconnecting said bodies, at least one of said bodies being comprisedof a porous element which allows penetration of steam there through andinto said primary chamber, wherein said porous element has one or moreporous and external surfaces that are substantially arcuate in form, ortwo or more porous and external surfaces, whereby steam can penetratesaid porous element from a plurality of different directions; indicatormeans being provided between said bodies at some location within theprimary chamber, said indicator means having a characteristic whichchanges while in the presence of steam and temperature after apredetermined time; and tortuous path means provided internally of thedevice, sealingly dividing the primary chamber into two secondarychambers, a first secondary chamber being defined between the tortuouspath means and an inner surface of said at least one body through whichsteam having permeated said body emerges, and a second secondary chamberbeing defined to the alternate side of said tortuous path means from thefirst secondary chamber and having the indicator means disposed therein,the tortuous path means having a single entry port in communication withthe first secondary chamber and a single exit port in communication withthe second secondary chamber, said steam being substantially constrainedto flow from the first secondary chamber through the single entry portinto and around said tortuous path means and then through the singleexit port before emerging into the second secondary chamber.
 2. A deviceaccording to claim 1 wherein the one or more porous and externalsurfaces are substantially arcuate in form.
 3. A device according toclaim 2 wherein said at least one body is cylindrical.
 4. A deviceaccording to claim 2 wherein said at least one body is at leastpartially spherical.
 5. A device according to claim 2 wherein the one ormore porous and external surfaces of the porous element aresubstantially continuous around at least one axis of the device.
 6. Adevice according to claim 1 wherein the pair of bodies connectedtogether to form the device both have a predetermined degree ofporosity.
 7. A device according to claim 1 wherein each of the pair ofbodies is substantially hemispherical.
 8. A device according to claim 1wherein at least one of the bodies is provided internally with acavernous recess to increase the effective volume of the primarychamber.
 9. A device according to claim 8 further comprising apertureddiaphragm means provided to sealingly define a tertiary chamber withinthe device in which steam can collect.
 10. A device according to claim 1wherein the pair of bodies are manufactured from a sinteredpolypropylene material.
 11. A device according to claim 1 wherein thedevice is reusable upon replacement of the indicator means.
 12. A deviceaccording to claim 1 wherein the porous element has two or more porousand external surfaces.
 13. A device according to claim 1 wherein theporous element comprises substantially the entire surface on one or bothof said bodies.
 14. A sterilizer test device comprising: at least a pairof bodies releasably and resealably connected together defining aninternal primary chamber within the device to which access is gained bydisconnecting said bodies, at least one of said bodies being comprisedof a porous element which allows penetration of steam there through andinto said primary chamber, wherein said porous element has one or moreporous and external surfaces that are substantially arcuate in form andsubstantially continuous around at least one axis of the device, wherebysteam can penetrate said porous element from a plurality of differentdirections; indicator means being provided between said bodies at somelocation within the primary chamber, said indicator means having acharacteristic which changes while in the presence of steam andtemperature after a predetermined time; and tortuous path means providedinternally of the device, sealingly dividing the primary chamber intotwo secondary chambers, a first secondary chamber being defined betweenthe tortuous path means and an inner surface of said at least one bodythrough which steam having permeated said body emerges, and a secondsecondary chamber being defined to the alternate side of said tortuouspath means from the first secondary chamber and having the indicatormeans disposed therein, the tortuous path means having a single entryport in communication with the first secondary chamber and a single exitport in communication with the second secondary chamber, said steambeing substantially constrained to flow from the first secondary chamberthrough the single entry port into and around said tortuous path meansand then through the single exit port before emerging into the secondsecondary chamber.